In the related art, as a propeller fan that is included in an outdoor unit of an air conditioner, an air cleaner, a ventilator or the like and is used for fluid feeding of air or the like, it has been known a propeller fan formed, using a fiber reinforced plastic (FRP) in which a glass fiber or the like is mixed with a thermoplastic resin such as an acryl resin at a predetermined rate (for example, 30 weight %), through an injection molding by setting molding conditions such as an injection pressure and a metal mold temperature to predetermined values.
FIG. 5 illustrates a general injection molding machine 110 that is used for the injection molding of the above-mentioned propeller fan. The injection molding machine 110 includes an injection unit 111 that melts a resin material serving as a material in order to inject the resin material, a metal mold 112 that molds the molten resin from the injection unit 111, a mold opening and closing mechanism 113 that closes the metal mold 112 after molding, and a projection mechanism 114 that projects the molded article to release the molded article from the mold after opening the mold.
Next, a molding machining sequence using the metal mold 112 will be described based on FIGS. 6 to 8. As illustrated in FIG. 6, the metal mold 112 is a three piece type metal mold including a stationary mold 121, a mobile mold 122, and an intermediate metal mold 123 located between both of them, and a plurality of projection pins 124 driven by the projection mechanism 114 is placed on a back side of the mobile mold 122.
Moreover, in a state of joining the stationary mold 121, the mobile mold 122 and the intermediate metal mold 123 at a predetermined clamping pressure, the molten resin is injected from the injection unit 111 into a cavity, not illustrated, formed between the mobile mold 122 and the intermediate metal mold 123 through a runner, not illustrated, formed throughout the stationary mold 121 and the intermediate metal mold 123, and thereby a molded article corresponding to an internal surface shape of the cavity is formed.
FIG. 7 illustrates a state of mutually separating the stationary mold 121, the mobile mold 122 and the intermediate metal mold 123 after molding to open the mold. Due to the opening of the mold, a molded article 116 molded in the cavity remains in a state of being attached to a molding surface of the mobile mold 122, and a runner portion 117 solidified in the runner remains in a state of being attached to the stationary mold 121 side.
In a state of opening the metal mold 112, as illustrated in FIG. 8, the projection pins 124 are caused to advance, the molded article 116 is separated from the mobile mold 122 by the projection pins 124, and the runner portion 117 is separated from the stationary mold 121. The molded article 116 manufactured in this manner is a propeller fan 101 serving as a molding object illustrated in FIG. 3. Furthermore, the injection molding state of the propeller fan 101 in the metal mold 112 is illustrated in FIG. 4.
As illustrated in FIG. 3, the propeller fan 101 has a peripheral wall 105 and an end surface wall 106, and includes a hub 102 which is approximately cylindrical with a bottom provided with a boss 104 for inserting a driving shaft of a motor, not illustrated, configured to rotate the propeller fan 101 in a central portion of the end surface wall 106, and three blades 103 having the same shape integrally attached onto the peripheral wall 105 of the hub 102. As mentioned above, the propeller fan 101 is manufactured by the injection molding using the injection molding machine 110 including the metal mold 112 illustrated in FIG. 4.
As illustrated in FIG. 4, when joining the mobile mold 122 with the intermediate metal mold 123, a cavity 127 is formed between the mobile mold 122 and the intermediate metal mold 123. Furthermore, when joining the stationary mold 121 with the intermediate metal mold 123, a runner 128 for supplying the molten resin injected from an injection nozzle 111a of the injection unit 111 to the cavity 127 is formed between the stationary mold 121 and the intermediate metal mold 123.
Furthermore, the shape of the cavity 127 is set so that a molding surface 125 of the mobile mold 122 side forms a positive pressure surface 103a of the blade 103, and a molding surface 126 of the intermediate metal mold 123 forms a negative pressure surface 103b of the blade 103 in consideration of mold release characteristics of the hub 102. Furthermore, as illustrated in FIG. 3, the runner 128 forms a three-pronged branched road shape corresponding to the number of the blades 103 of the propeller fan 101, and a downstream end of each branched road of the runner 128 is a gate 129 serving as an injection hole of the molten resin into the cavity 127.
Thus, the molten resin is injected into the cavity 127 through the runner 128 from the injection nozzle 111a at a predetermined injection pressure, the cavity 127 is filled with the molten resin, and thereby the propeller fan 101 having a shape corresponding to the inner surface shape of the cavity 127 is molded.
At this time, the runner portion 117 having a shape corresponding to the inner surface shape of the runner 128 is molded in the runner 128 by the molten resin supplied thereto, and the runner portion 117 is integrally connected to the propeller fan 101 by each gate 129. The propeller fan 101 and the runner portion 117 are cut and separated by each gate 129 when the metal mold 112 is opened. Thus, as illustrated in FIG. 3, cutting traces in the runner portion 117, that is, three gate marks 118 remain on the end surface wall 106 of the propeller fan 101 after the molding.
However, in general, since the shape of the blade of the propeller fan greatly affects the blowing performance, the shape is designed under extremely exact calculations, and thus there is a need to pay a close attention so as to obtain the shape of the blade corresponding to the design shape, particularly when manufacturing the propeller fan.
For example, when setting the gate 129 of the runner 128 to a position corresponding to a blade surface (the negative pressure surface 103b illustrated in FIG. 4) of the blade 103 of the cavity 127, the gate marks 118 remain on the blade surface of each blade 103 of the molded propeller fan 101, the blade surface becomes uneven due to the presence of the gate marks 118, the blade surface shape is different from the design shape, and thus the blowing performance may decline.
Thus, in the related art, generally, as illustrated in FIGS. 3 and 4, each gate 129 is set to a position corresponding to a root of the blade 103 of the peripheral wall 105 on the end surface wall 106 of the hub 102 while avoiding the provision thereof on the blade 103 side.
Furthermore, the shape of the propeller fan of the related art and the manufacturing method thereof mentioned above is, for example, described in the description of the related art in Patent Literature 1.
However, in the propeller fan of the related art mentioned above, the number of the gates 129 at the time of the injection molding is one with respect to each blade 103, as illustrated in FIG. 9, the molten resin that flowed into the cavity 127 from the gate 129 flows like the flow of the resin indicated by reference numeral 400.
Specifically, the molten resin that flowed into the cavity 127 from the gate 129 flows so as to spread in the cavity 127 from the gate 129, and flows like the flow 400 (400a to 400f) of the resin illustrated in FIG. 9. Although the blade 103 is jointed to the peripheral wall 105 of the hub 102 by a root portion 200, as illustrated in FIG. 4, a thickness from a root portion 200 to the leading end portion of the blade 103 becomes thinner toward the leading end portion of the blade 103 from the root portion 200.
The molten resin that flowed from the gate 129 initially reaches the root portion 200 just below the gate 129 (the gate mark 118). The molten resin that reaches this then flows in a direction along the root portion 200, that is, like the flows 400a and 400b of the resin illustrated in FIG. 9 before flowing in the direction of the blade 103 for a difference in thicknesses from the above-mentioned root portion 200 to the leading end portion of the blade 103. Moreover, the molten resin that reached the root portion 200 by other courses is pressed into the flows 400a and 400b of the resin, and flows in a direction along the root portion 200 like the flows 400c to 400f of the resin illustrated in FIG. 9.
The molten resin is a fiber reinforced plastic, and includes a continuous fiber 300. However, since the orientation direction of the continuous fiber 300 is parallel to the flow of the resin, the orientation direction thereof is oriented in a direction along the root portion 200 by the above-mentioned flows 400a to 400f of the resin. There is concern that cracks may occur in the root portion 200 in the direction along the root portion 200 due to force applied to the root portion 200 when rotating the propeller fan 101. However, when the occurrence direction of the cracks is equal to the orientation direction of the continuous fiber 300, strength of the force applied to the root portion 200 is degraded. Thus, when rotating the propeller fan 101, the blade 103 might break in the root portion 200 at a relatively low revolution number (for example, 2,500 rpm).